Aerofoil



J. V. MARTIN.

AEROFOIL. APPLICATION FILED NOV 30. 1917.

3 SHEETS-SHEET I.

ATTOR/Vfy Patented Dec. 13, 1921.

J. V. MARTIN.

AEROFOIL. APPLICATION FILED NOV 30, 1917.

11111-111911 Dec. 13, 1921.

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V 7 CL 2 M n x I I b 0 w n 5 AH n 6 u w. 3 W 1 J. V. MARTIN.

AEROFOIL. APPLICATION FILED NOV. 30, I917.

Patented Dec. 13, 1921.

3 SHEETS-SHEET 3 My M2 WI TNESS:

d m Z 27 ATTORNEY UNITED STATES I JAMES V. MARTIN, OF ELYRIA, OHIO.

AEROFOIL Specification of Letters Patent.

Patented Dec. 13, 1921.

Application filed November 80, 1917. Serial No. 204,602.

To all whom it may'concern:

Be it known that I JAMES V. MARTIN, a citizen of the United states, and resident of Elyria, in the county of Lorain and State of Ohio, have invented certain new and useful Improvements in Aerofoils, of which the following is a specification.

The invention relates to an aerofoil for use on any type of aeroplane construction. It is to be understood that the term aerofoil used herein is of suflicient breadth to include any body projected through the atmosphere for an aerodynamic reaction.

The primary object of the invention isto provide a form-of aerofoil which will have a maximum-K or. lift, and a minimum K ordrift coefficient, or a maximum lift-drift ratio at one angle of incidence and which has a relatively slow rate of change from said maximum lift-drift ratio when'the aerofoil is moved from said angle of incidence.

I attain this object broadly by providing an aerofoil of a double convex form with its longitudinal chord extending from the leading to the rear edges, disposed within the outlines of the aerofoil and with its longest ordinate intersecting the chord approximately at the center ofpressure of the aerofoil.

Another object of the invention is tov provide an aerofoil which can be braced internally to withstand the strains incidental to high pressures thus eliminating practically all external bracing.

A still further object of the invention is to provide a type of aerofoil which will minimize interference from a superimposed aerofoil and which will tend to preserve a relatively high lift to drift ratio in' the presence of any superimposed aerofoil.

Various other objects and advantages of the invention will be in part obvious from an inspection of the accompanying drawings and in part will be more fully set forth in the following particular description of one form of structure embodying my invention, and the invention also consists in certain new and novel features of construction and combination of parts hereinafter set forth and claimed.

In the accompanying drawings:

Figure 1. is a plan view looking down upon one of the aerofoils shown in section in Fi 3 to 6' and illustrating a preferred embodiment of my invention.

' Fig. 2 is a vertical sectional view taken aerofoil.

longitudinally of the aerofoil and on the lineshown in Fig. l is relatively wide across the line of flight compared with its length in the direction of its-line of flight. The front or leading edge is defined by a leading edge bar 10 disposed parallel to the rear or trailmg edge defined by a rear edge bar 11. Opposlte side edges 12 recede from the front toward the rear edge as shown in Fig. 1.

Referring to any of the forms shown in Figs. 3 to 6, it is seen that the aerofoil includes an upper skin surface 13 and a corresponding lower skin surface 14, curving-in a general double convex curve from the leading edge 10 to the rear of trailing edge 11.

he curvature of these surfaces is of prime importance in this disclosure. For the purpose of establishing points of reference for these curves, it is to be considered that vertical sections taken through the aerofoil from front to rear are of the general form shown -in these figures. The aerofoil is so positioned that its longitudinal chord or center line indicated by the dotted line 15 extends from the leading to the rear edge and is contained entirely within the outlines of the The surfaces are symmetrically positioned with reference to the chords, that is, the longest ordinate on one side is in line with the longest ordinate on the other side of the chord, and correspondingly the correlated ordinates across the chord decrease in the same ratio toward ends of the chord.

The surfaces are so disposed that the greatest thickness of the aerofoil is approximately one-third of the length of the chord spaced from the leading edge 10. This portion of greatest thickness is preferably positioned at the center of pressure on the aerofoil, herein indicated by the lines 0 By this arrangement it is possible to dispose the greatest amount of internal trussing at the point on the aerofoil which is subjected to the greatest distorsional strains.

For the purpose of defining mathematically one preferred form of curve for the upper profile at 13 in Figs. 36, reference is made to the resultant curve found in Fig. 8 which may be plotted as follows:

Draw upper half of arabola VCE, whose equation is 3 =.187I X, about the axis X-X, where K is a constant equal to the chord of the aerofoil selected.

Draw axis Y-Y normal to X-X at V. Draw axis A-A at an angle of 20 to X-X, intercepting it at a distance -.2 38 K from Y-Y.

Erect a perpendicular to X-X at B, a distance of .061K from Y- Through the intersection of this line with A-A draw a line 0-0 normal to'A-A.

Erect ten perpendiculars to A-A, a distance of .lK apart with the first perpendicular spaced fromO O adistance of .lK.

Draw H-H normal to A-A, a distance of .0074K from 0-0.

Draw J-J normal to A-A, a distance of -.0015K from 10 10.

Draw CCnormal to X-X at C, a distance of .622K from ,Y-Y, intercepting 6-6 and parabola VCE at C.

Draw the arc-of a circle R (whose equation is m +y =.000054.-76K referred to the coordinate axes A-A and H-H) beginning on axis A-A and terminating at the parabola VCE. This circle will be osculatory to 0-0 and VCE. This will be the first part of the upper profile.

The are of the parabola VCE, (whose e nation is y =.187KX referred 'to axes -X and Y-Y), included between the lines H-H and'6-6 will be the second part of the profile.

At point C on 6-6 draw a tangent (whose equation is Y=K (.038X+.191), referred to the coordinate axes X-X and Y-Y), to the parabola VCE, and terminating at J-J. The straight line included between 6-6 and J-J is'the third part of the profile.

Draw the arc of a circle R (whose equa tion is X +Y =.00OOO225K referred to coordinate axes A-A and J-J), beginning at the tangent CR and terminating on axis A-A. This circle will be osculatory to CR and 10-10. This is the fourth and final part of the profile.

The curve so formed will respond to the upper curve of the aerofoils shown in Figs.

5 to 6 inclusive and also, when reversed, to the lower curve of the aerofoil shown in Fig. 3.- The lower profile of the form shown' in Fig. 4 is a locu whose ordinates are threefourths of the ordinates file. The lower profile of the form shown in Fig. 5 is a locus whose ordinates are onehalf of the ordinates of the upper profile and similarly the profile of the form shown in Fig. 6 1s a locu whose ordinates are onefourth of the ordinates of the u per profile.

As shown in Fig. 1 the aerofoii mcludes an of the upper prointernal framework formed of a plurality of win bars in addition to. the leading and trai ing edge bars 10 and 11. These wing bars extend lengthwise in parallel relation and are spaced across the width of the aerofoil. The internal wing bars intlude a main wing bar 16 and a rear wing bar 17. The

wing bars are box-formed structures combining lightness with strength.

As shown in .Fig. 7, the wing bars are formed of two stress boards, an upper tension board 18 and a lower compression board 19 with an upstanding web board 20. extend in therebetween and fitted into the top and bottom boards to form in effect an I beam construction. Filler blocks 21 are positioned on opposite sides of the web board and between the flanges formed by the extensions of the stres boards 18 and 19 on opposite sides of the web board. If desired the main bar may be additionally strengthened winfg by astening-metal plates 22 to opposite sides of the web board. A plurality of' transversely spaced and longitudinall extending ribs 23 are positioned edgewise between the leading and trailin edge bars and normal to the wing bars. These ribs give the aerofoil the profile shown in Figs. 3 to 6. Certain of the ribs 24 are enlarged and strengthened suflicient to act a struts, and all of the ribs have a de th sufiicient to permit the wing bars to lieassed therethrough lyas shown in Fig. 2. airs of diagonal: straps 25,- preferably piano tween adjacent struts rnd coact therewith to take up the drift stresses on the aerofoil when theplane is in motion. One end of each of the straps is attached to the lowerportion of one of the struts adjacent the leading ed e bar and the other end is attachedtot e upper portion of the next adjacent strut at t e conjunction of this next strutwith the rear wing bar.

While I have shown and described, and

have pointed out in the annexedclaims, certam novel features of my invention, it will wires, arestretc'hed belustrated and in its op-' normal upper and lower surface forming parabolic curves, the chord of said" curves extending in the general direction of flight of the aerofoil, the parabolic curve formed by the central portion of upper surface being of the form approximatin the curve indicated by the formula 3 =.18 KX where is a constant equal to the chord of the aerofoil.

2. A double convex aerofoil having its chord extending approximately in the line of flight of the aerofoil and positioned be tween the normal upper and lower surfaces thereof, the upper and lower surfaces being symmetrically curved relative to each other from the leading to-the trailing ed and a considerable part of the centra ortion being parabolic and of the class having the formula g =0.187KX, where K is a constant equal to the chord of the aerofoil.

3. A double convex' aerofoil having its chord extending approximately in the line of flight of the aerofoil and positioned between the normal upper and lower surfaces thereof, the upper and" lower surfaces being each of the same species of curvature relative to each other from the leading to the trailing edge, the surfaces being so positioned that the ordinates below the chord are fractional parts of the corresponding ordinates above the chord, the ratio between the arts of certain ordinates above the chord and the corresponding parts below the chord being the same for a plurality of the ordinates spaced a material distance along the'lengt-h of the chord.

4. An aerofoil having a profile, the major portion of which is parabolic and of the class having the formular y =O.187KX, where K is-a constantxequal to the chord of the aerofoil.

5. An aerofoil having a profile, the major portion of which is parabolic and of the class having the formula y'-=0.187KX, where K is a constant equal to the chord of the aerofoil, and another portion of which is a tangent osculatory to the parabolic porportions.

the parabolic portion and a thirdportion circ ar and osculatory to one of the other 8. An aerofoil construction having a pro- .file on one side of the chord formed in order from front to rear of a circular portion, a parabolic portion, a flat portion and=a circular portion.

9. An aerofoil construction havin a profile on one side of the chord formed in order from front to rear of a circular portion, a

arabolic portion, a flat portion and a circuar portion, and having a profile on the other ordinate whereby there will be a the length of the part of each ordinate below the. chord is less than the length of the part thereof above the chord and the ratio between said lengths of any one ordinate being substantially the same for all other ordinates along a material length of the chord.

11. A double 1 convex aerofoil with its chord contained within the upper and lower surfaces, said surfaces being spaced from the chord with the longest ordinate on one side of said chord being in line with the longest ordinate on the other side of the chord, the correlated ordinates across the chord decreasin in the same ratio toward one end of the cord, the lower ordinates in each case being of. less length than the corresponding upper ordinate whereby there will be a greater thickness of aerofoil part above the chord than below the chord.

12. A double convex aerofoil with its chord contained within the upper and lower surfaces, said surfaces being spaced from the chord with the longest ordinate on one side of said chord being in line with the longest ordinate on the other side of the chord and positioned above one-third of the length of the chord from the leading edges, the cor related ordinates across the chord decreasing in the same ratio toward one-end of the chord, the lower ordinates in each case being of less length than the corresponding upper greater thickness of aerofoil part above the chord than below the chord.

13. A double convex aerofoil having relatively sharp leading and trailing edges and with its chord intersectin said edges, the length of the part of eac ordinate below the chord being approximately one-fourth of the length of the corresponding part above the chord.

14. A double convex aerofoil having its chord contained between the upper and lower surfaces, the profile of the major portion of both of said surfaces being parabolic, the length of the parts of the ordinates below the chord being each a fractional part of the length of thearts of the corresponding ordinate above t e chord, said fractional part being substantially the same for the ordinates along a considerable part of the chord.

Signed at New York in the county of New York and State of New York this 17th day of August, A. D. 1917.

JAMES V. MARTIN.

I DISCLAIMER 1,4 O0,177-.Ja me;a V. Martin, Elyria, Ohio. A-ERoFoIn. Patent dated December 13, 1921. Disclaimer filed February 26, 1937, by the patentee.

Hereby enters this disclaimer to the following words appearing at page 1, lines 8 to 13 of the specification which your petltioner desires to erase from said specification:

Theinvention relates to an aerofoil for use on any type of aeroplane construction. It is to be understood that the term aerofoil used herein is of sufficient breadth to include any body projected through the atmosphere for an aero-dynamic reaction.

and hereby disclaims the invention set out in claims 1 to 14 of said patent except when the aerofoil is the wing of an aeroplane.

[Oflicial Gazette March 30, 1937] 

